Traffic signaling system



Search Room 8 Sheets-Sheet 1 Filed April 12, 1941 HRN mukm nur lNVENTOR ATTORN EY sm'ch Hoon Jan. 11, 1949. w. s. HALSTEAD 2,459,105

TRAFFIC SIGNALING SYSTEM Filed 'April 12, 1941 s sheets-sheet 2 S g a N -1 \o\ a.

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/z//LL/AM HALsrfAa INVENTOR ATTORNEY Jan. 1l, 1949. w. s. HALSTEAD TRFFIC SIGNALING SYSTEMy a shets-sneet s Filed April 12, 19414 MJINIRN INVENTOR.

ATTORNEY.

:1151 ifm bijl-l Jan. 11, 1949. w. s. HALs'n-:AD 2,459,105

TRAFFIC SIGNALING SYSTEM Filed April 12, l1941 8 Sheets-Sheet 4 INVENTOR.

ATTORNEY.

W. 4S. HALSTEAD TRAFFIC SIGNALING SYSTEM Jan. 1l, 1949.

8 Sheets-Sheet 5 Filed April 12, 1941 soz FIG. 6.

FIG. .5.

ATTORNEY Mmm Jan- 11, 1949- w. s. HALsrEAD TRAFFIC SIGNLING SYSTEM 8 Sheets-Sheet 6 Filed April 12, 1941 www N .UHRN

INVENTOR.

BY d M ATTORNEY.

Jan- 11, 1949. w. s. HALSTEAD TRAFFIC SIGNALING SYSTEM 8 Sheets-Sheet 7 Filed April 12, 1941 www .mzmmmmm- 2971s.@ .27716./0 FIC-7.1i.

A//LL/AM /usnma INVENTOR ATTORNEY W. S. HALSTEAD TRAFFIC SIGNALING SYSTEM Jan. 11, 1949.

8 Sheets-Sheet 8 Filed April 12, 1 941 FIG. f2.

A/ML/AM 152 Hasn-Ab INVENToR ATTORNEY iJULJiiIi; il?

UNITED STATES PATENT oFi-icE TRAFFIC SIGNALING SYSTEM William S. Halstead. Purchase. N. Y., assigner, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application April 12, 1941, Serial No. 388,338

4 Claims. (Cl. Z50-6) This invention pertains to traflic signalling, and invention to freight classification service. 'Ilhis in particular relates to a traffic control and comapplication, therefore, does not constitutea limmunications system of the general type as disitation since the flexibility of the system is such closed inthe Halstead Patent No. 2.l31,042,issued that it may be used in signalling zones along September 27, 1938. i' railway main lines, in various terminal areaspor The system of the Halstead patent involves iii other vehicle communications and traffic sigthe use of electric carrier wave energy for comnailing services. municating intelligence to traic within prede- The present embodiment of the invention emtermined signalling zones by means of speech braces a coordinated aural-visual communicasignals and audio frequency control signals which l" tions and signalling system constantly under suseive to selectively actuate visual indicators, such DCI'VSOl'y 4COIitl'Ol 0f alliOmRliC DIOCCLVG, 01' as stopf goj or caution signal lights. lThe Checking signa' circuits. Carrier wave energy. audio frequency control signals may also so be modulated b v voice and control signals, is transrendered audible, to serve as an sum1 check, by mitted from a control station to vehicles within means of the same electro-acoustic apparatus V naiven signalling zone. Receiving equipment on that is employed for reproduction of the speech all vehicles within the zone, may, if desired, be signals, tuned to respond to carrier wave -energy, of a The present application incorporates certain of Dledetclmllied ZOU@ I'HlUCUQy. which 1S transthe principles disclosed in the original system lnittrd from the Control Station. Thus, the 0nand includes improvements and modifications for 3" Cl'ili'Ol' 0f iii@ COIiiilOl Station may be the Central effecting twway aural communications as wel] coordinator of all movements of vehicles, such as protective visual and aural signalling, for the as locomotives, within the signalling zone. 'lhis purpose of attaining positive` centralized control Zone. in the CRS@ 0f ClaSSiiiCation yard signalling. cf traffic operations within a given signalling may extend from the transmitter in every dlrecz0ne J5 tion throughout. a yard area, or it may be local- In app1ying the system 0f the Haistead patent ized along specific lanes of trailic by directional to specilic trailic signalling elds, an example wave-energy transmitting systems as disclosed in of which may be that of classification yard sigthe Haitelfi Patent. nailing, certain modifications and improvements In Ol'del i0 more Completely ensure efficient have been found to be desirable in order to more :lo and safe opclatiOn 0f Vehicles Within the Sig- @nectively adapt the Originm system to the connailing area, automatically-transmitted periodic ditions peculiar lo the particular service. For ChCkin.Z" Signal indiCatiOrlS are provided in example, it has been determined that twoway both the control station and in vehicles. This aural communications between a central point Del'mii' COHDUOUS SUpGlViSiOn 0f Operation Of and operators of vehicles, such as locomotives, or :i5 COi'lii'Ol transmitter equipment and receiving motor trucks, within a terminal area is desirable, units in all vehicles as will be described in further and that constant periodic transmission of a detail. protective aural and visual checking signal at It is essential in any trailic .signalling and compredetei'mined intervals is of particular value in niunication system in which orders of any na- .'prevcnting damage to equipment or operating rio ture are periodically transmitted to moving vehil{personnel in the event of failure of the control i' cles to provide a means for the pievention ol ,il station transmitter or vehicle receiving equipaccidents which might result from failure of the fl? ment. Also, it has been found desirable to pro-i/i transmission and reception equipment. Suppose,

i for exampe. that a control dispatcher has given aural proceed instructions to the engineer ol' l a pusher locomotive located at the rear of a long freight train proceeding towards the hump eration while signals are being received from the of a classiiication yard. Under these conditions, remote transmitter. particularly if wayside signals are obscured by Although the system of the present invention 50 a fog or storm, the engineer will continue to vide an automatic control means, operable by?! wave energy transmitted from a remote trans-il' mittei, which may be on a vehicle, whereby that control station transmitter is locked-out of op-,J

iis particularly applicable to signalling in large move the locomotive until another signal is re terminal arcas, such as classification yard, the ceivcd to caution him or to direct him to cease embodiment of the invention as described herein the movement, Shoud the control transmitter is illustrative only, and represents a specic exor locomotive receiving apparatus fail, the engiample of thc application of the system of the 'l neer would assume that lic should continue to move even though, in the meantime. the control operator has issued instructions to stop. It is obvious that the dispatchers instructions would be ineffective in bringing the locomotive to a stop, not being aware of failure of equipment. Under this condition a serious accident might result.

Thus, in order that the engineer may ascertain at all times that the central station trans mitter and locomotive receiver are in proper working order, an over-all protective checking system of automatic type is incorporated in the novel control means of the present invention. This checking system operates, in a general sense, upon the closed circliit principle in that failure of any part of the signalling system will automatically be indicated.

The checking system comprises a continuously operative means for transmitting a periodic control signal of a particular -form which may be received by the engineer to indicate that he is receiving signals from a central station.

In the illustrative embodiment of the invention described herein, the control station emits a carrier frequency, modulated by a particular audio frequency which is transmitted periodically to the engineer. This signal is preferably in the form of a periodic series of impulses which may be manifest in the engineers cab by aural or visual means.

This periodic carrier signal modulated by voice signals or by a particular control frequency may be employed at the mobile receiver to energize a sound reproducer or to selectively energize a particular checking or proceed indicator lamp in order that the engineer may know that he is in contact with the control station and may proceed in safety with a given order. During the transmission of speech from the central station, it is desirable that the checking system cease to operate in order that an uninterrupted intelligible voice signal may be received. To effect this function, the present invention employs a selective control circuit which automatically dispenses with the checking or proceed signals when the central transmitter operating switch is closed.

When the engineer desires to acknowledge the receipt of a particular control signal, he may, by means of his transmitter, send back a signal to the control station. This may be accomplished by voice signalling from the mobile unit, or by the simple closure of the transmitting switch in accordance with a predetermined code, which, when received at the control station, will automatically cause the visual operation of a carrier-actuated signal light.

In order to prevent interference with reception of a voice signal from a locomotive transmitter by the periodic actuation of the central control transmitter, a novel, carrier-actuated lock-out circuit is employed to automatically preclude operation of the central station transmitting operation and to keep the central station receiver in its normally-on condition while a carrier signal is being received. This lock-out circuit also serves to prevent manual operation of the central transmitter as long as a carrier wave from a locomotive transmitter is being received. A visual indication of reception of a carrier wave from a locomotive transmitter is also provided for supervisory or acknowledgment purposes. Thus, by means of automatic controls and visual signal indicators, a coordinated signalling system of highly dependable nature is provided. The possibility of simultaneous operation of both central station and mobile transmitter is also removed.

It is an object of this invention to provide a novel traflic signalling system for transmitting speech and protective control signals to trafiic within a signalling zone.

It is an additional object of this invention to provide a novel two-way traffic communicating system for transmission and reception of visual and aural control signals within a signalling zone.

It is a further object of this invention to provide means whereby a control signal from a first electric wave transmitter will lock-out and prevent operation of a second remote transmitter while said first transmitter is emitting its lockout control signal.

It is another object of this invention to provide means whereby a periodic control signal is automatically emitted at predetermined intervals from a signal transmitter at one station to a cooperatreceiver at a second remote station to serve as a checking, or supervisory, signal for indicating that said transmitter and said receiver are operative.

Another object of this invention is to provide a trafiic communications and control system for coordinating the movements of vehicles in a traffic area which is effective to automatically indicate failures in the transmission and reception system.

Another object of the invention is to provide for a comprehensive traffic control system for a railroad freight classification yard or similar terminal area wherein each of the locomotives or other vehicles is adapted to receive and transmit control signals, each relating to a particular freight yard operation.

While these objects have been set out specifically herein, it is to be understood that they are illustrative, and that other objects may be, or may become, apparent to a person skilled in the art from a perusal of the present disclosure without departing from the spirit of the invention as presented in the sub-joined claims.

Referring to the drawings:

Figure 1 is a block diagram of the transmitting and receiving equipment employed at a central control station disposed adjacent a trafilc signalling zone.

Figure 2 is a block diagram of transmitting and receiving equipment employed in a locomotive or other vehicle operating within the signalling zone of the central control station.

Figure 3 is a circuit diagram of transmitting equipment employed at the central control station.

Figure 4 is a circuit diagram of a present-employed receiver utilized at the central control station.

Figure 5 is a iront elevational view of one preferred arrangement of a microphone, signal lights, and a loudspeaker disposed at the central control station.

Figure 6 is a side elevational view of the apparatus shown in Figure 5.

Figure 7 is a circuit diagram of a present-employed transmitter and receiver installed on a locomotive within the signalling zone of the central control station.

Figure 8 is a circuit diagram of a two-channel audio-frequency lter and checking-signal control relay and loudspeaker circuit employed in the present embodiment of the invention.

Figure 9 is a front elevational view of a presentpreferred arrangement of a microphone, signal 5 lights, and exible supporting arm employed in the locomotive.

Figure 10 is a front elevational view of the microphone and signal light unit of Figure 9 with the front cover removed.

Figure ll is a side elevational view of the microphone and signal light arrangement, showing the disposition of a shock-mounted microphone and signal lights within a housing such as illustrated in Figure 9.

Figure 12 illustrates a present-preferred disposition of voice and protective signalling equipment of the system within a locomotive cab.

Referring now more particularly to Figure 1, there is shown a schematic representation of the central control station transmitter and receiver. This gure is merely a diagrammatic represent-ation of the more detailed circuit diagrams shown in Figures 3 and 4 and the following description of the component parts vxill correspond for all of these figures.

The central control station may be located in the most accessible point of the limited area over which coordinating signals are to be transmitted.

Thus, if the system to be described is applied to a r freight classification yard, the central station may be disposed most conveniently adjacent the hump. The transmitter and receiver at the hump may be remotely controlled from one or more points if desired.

From these control points, the hump conductor, yard master or other control station operator may be in a position to best determine the nature of the signal to be transmitted to locomotives equipped with coacting signalling apparatus, which may be of the form diagrammatically illustrated in Figure 2 and more particularly in the circuit diagrams of Figures 7 and 8.

Essentially, the central station includes a. combined transmitter and receiver for establishing two--way voice co-mmunications and automatic protective signalling with locomotives or other vehicles operating within a given signalling zone, such as the classification yard area..

As is illustrated in the embodiment of the invention shown in Figure 1, a receiver 2| and a transmitter 22 utilize a single antenna 23 which is joined to the transmitter or receiver through an antenna transfer relay 24. The receiver 2| may comprise conventional equipment for demodulating and amplifying a modulated signal radiated from the antenna 5| which is energized by a transmitter 52 i Figure 2) disposed upon a locomotive or a similar vehicle. The signal radiated from antenna. 5| is intercepted by antenna 23 at the central station and applied to the receiver 2| (Figure 1) which in turn applies the demodulated signal energy to a loud speaker 25 for rendering the received signals audible.

The transmitter 22 at the control station may also comprise conventional equipment for amplifying electrical signals impressed upon the input circuits .thereof and causing these signals to modulate a radio frequency carrier which is then radiated into space through antenna 23 for reception by antenna 5| of Figure 2 and its coacting receiver 53 disposed upon a. movable vehicle.

The signals applied to the input of transmitter 22 may comprise voice currents generated in microphone 26 or a constant-amplitude audio frequency control signal generated at source 2l for utilization by protective checking apparatus at the central station illustrated in Figure l and corresponding apparatus at the movable station indicated in Figure 2 for constantly providing f Til periodic indication of the proper operation of all these circuits.

This audio frequency control signal is coupled to the transmitter through a transfer relay 3| which is manually controllable by a suitable switch such as the foot switch 32. Under` normal conditions, the transfer relay 3| is in a position where the audio frequency energy from signal source 21 may be applied to the input of the transmitter 22. The antenna transfer relay 24 is normally in a position for applying the signals intercepted by antenna 23 to the receiver 2|.

The receiver 2| and transmitter 22 are eneigized from any available power source which may comprise batteries or alternating current. Tho filaments of the various vacuum tubes utilized in these circuits are continuously energized whereas the plate circuits of the transmitter and receiver are selectively energized from a high voltage source connected with either the transmitter or the receiver through the power transfer relay 33.

The movable members of the power transfer relay operate simultaneously with the movable members of the ant-enna transfer relay 24. Thus when the antenna 23 is coupled to the receiver 2|, the power transfer relay applies the high voltage to the plates of the receiving tubes. Conversely, when the antenna transfer relay interconnects the antenna 23 and the transmitter 22. the power transfer relay serves to permit the energization of the transmitter vacuum tubes and to deenergize the plate circuits of the receiver 2|.

An automatic keying device 34 is continuously operated and under normal operating conditions determines the movement of the power transfer relay 33 and the antenna transfer relay 24, and effects periodic operation of the relays. The keying device 34 is employed to apply an energizing voltage to power transfer relay 33 and to antenna transfer relay 24 at regular intervals.

When this energizing voltage is applied to the relays. a signal is radiated which is a radio frequency carrier modulated by the constant-amplitude audio frequency control signal provided by the control signal source 21. This energizing voltage is of relatively short duration and thus the radiated checking signal is in the form of a plurality of periodic modulated impulses.

During the normal non-keying portion of the operating cycle of the keying device 34, the power transfer relay 33 and the antenna transfer relay 24, are in the normal position which, as previously mentioned, permits receiver 2| to reirain in a normally-on condition to accept incoming signais from a transmitter of the type indicated in lziigure 2. and to impress them upon loud speaker Accordingly, the central station during its operation transmits a series of periodic impulses and is in a position for receiving signals in the intervening time. If the operator of the central control station desires to transmit instructions to the vehicle carrying the apparatus illustrated in Figure 2, operating within the localized areas such as the freight classification yard, the switch 32 is depressed which in turn causes the operation of transfer relay 3|.

As previously described, the transfer relay 3|, when energized disconnects the modulating control signal source 2'| from the input circuit of the transmitter and couples the microphone thereto. In addition, the operation of transfer relay 3| energizes power transfer relay 33 and antenna transfer relay 34 to apply voltage to the transinitter plate circuits. and to couple the antenna 23 to the transmitter output circuits.

Thus, it may be seen that speech signals applied to the microphone 2'6 will be caused to modulate the output circuits of transmitter 22 and a modulated signal will be radiated from antenna 23. The central station circuits will be in a condition for transmitting speech signals as long as the switch 32 is closed.

When the desired instructions have been given by the control operator, the release of switch 32 will then automatically disconnect the microphone and apply the control signal generated within source 21 to the input circuits of the transmitter and the keying device 34 will again resume control of the sequential application of power to the plate circuits of the receiver and transmitter and the corresponding application of the antenna 23.

The central control station is provided with a plurality of pilot lights which indicate proper operation of the entire two-way communication system. These pilot lights are disposed in the operators ileld of vision to facilitate checking operations. A pilot light 35 is provided to indicate the fact that a modulated carrier is being radiated from antenna 23 during the operation of the transmitter. This is accomplished by a circuit which is inductively coupled to the transmitter antenna circuit.

As will be hereinafter explained, the signal induced in this circuit is applied to a demodulating and audiofrequency signal rectifying circuit 36 which causes the operation of a relay 31 when a modulated signal is being radiated. The relay 31 in turn energizes the transmitting monitor signal light 35. It is evident that during the normal operating cycle, the monitor light 35 will be energized periodically by the modulated lcarrier which is caused to be periodically transmitted by the keyer 34.

An additional visual indication for the operator of the central station is a transmitting indicator light 4| which is energized whenever the power transfer relay energizes the plate circuits of the transmitter 22. Accordingly, during the normal operation of the control station, the monitor indicating light 35 and the transmitting pilot light 4| will be energized in unison.

On the other hand, when the foot-switch 32 is operated for the transmission of speech, the transmitting indicating light 4| will be continuously energized to indicate the application of power whereas the monitor light 35 will flash in accordance with the impressed signal voltage during speech transmission or other modulation.

When antenna 23 is energized by signals from a vehicle operating within the classification yard or other such area, the receiver 2| operates to demodulate these signals and impress the demodulated energy upon loud speaker 25.

To prevent intereference with an incoming signal from a locomotive transmitter by the automatic or manual operation of the central transmitter, a novel carrier-operated transmitter lockout control circuit is provided which automatically causes the periodic keying circuit 34 and input transfer relay 3| to lose control over the operation of the power transfer relay 33 and the antenna transfer relay 24. This lock-out condition will exist as long as a carrier-wave from a locomotive transmitter is being received at the central station.

To eiect this control function a carrier-controlled lockout relay 42 is provided in the audio amplifying and noise suppression circuit of the receiver 2| and operates whenever a carrier is received by antenna 23 from a transmitter such as 52 indicated in Figure 2. This relay when energized automatically disconnects the keying device 34 and transfer relay 3| and thus permits the continuous reception of energy by receiver 2|. In order to provide an indication that a carrier wave is being received, the lock-out relay 42 also serves to energize an indicating light 43 which again is preferably disposed in the operators normal field of vision.

It is evident that this novel system provides means whereby signals from a vehicle may be received aurally through the agency of loud speaker 25 or visually by pilot light 43. Thus, since the lock-out relay is operated by an incoming carrier wave transmitted from the vehicle transmitter 52 illustrated in Figure 2, the operator of the vehicle may, by momentarily keying his transmitter 52 through the agency of a switch 54, transmit an intermittent carrier which will energize pilot light 43 in accordance with any predetermined signalling code of simple form. Thus the engineer may acknowledge receipt of an instruction, or convey other signal intelligence if it is not convenient for him to speak into his microphone.

Therefore, it may be seen that if the central station is arranged with the various circuit elements diagrammatically illustrated in Figure 1, it will continuously and automatically transmit a series of checking or control impulses and be in a position to receive signals in the time between impulses.

Furthermore, the central station operator may transmit any desired speech signals and may receive incoming signals aurally or visually. Thus the central station is equipped for two-way cominunication with a remotely disposed station such as that indicated in Figure 2. If this equipment is applied to a railroad freight classication yard, then the radio apparatus of Figure 2 may be most conveniently located within the cab of a locomotive or upon the tender thereof. Essentially, the mobile equipment comprises the transmitter 52 and receiver 53, each cooperable with the single antenna 5| through a relay 55 which selectively connects the antenna and the receiver or transmitter.

Normally, the transfer relay 55 is in a position where antenna 5| is coupled to receiver 53 so that signals radiated from antenna 23 at the control station will be applied to the receiving equipment at the locomotive. The received signals after being demodulated in receiver circuits 53 are applied to a two-channel lter 56 which may, as will hereinafter be pointed out, comprise a parallel combination of high and low pass electric wave lters.

The filter 56 selectively applies received speech signals to a loud speaker 51 for rendering such speech audible to the locomotive engineer. Furthermore, this lter 55 separates speech signals from the received periodic checking signals of predetermined audio frequency which are radiated by antenna 23 at the control station when the control station is operating periodically under influence of the automatic keying device.

Thus one channel of filter 55 is tuned to separate the audio frequency control signal energy from voice signals and to selectively apply this control signal energy to a rectifier 6| whichA in turn energizes relay 62 to produce a visual indication through the agency of a checking light 83.

Therefore this checking light will flash in accordance with the received audio frequency impulses in a manner similar to the monitor pilot light 35 at the control station. Accordingly, the checking light 63 disposed preferably within the field of vision will provide a visual indication by its flash that the central control station illustrated in Figure 1 and the locomotive receiving apparatus are in proper working order.

As a further assurance of this fact, a portion of the checking signal energy may be allowed to pass through the filter 56 to the loud speaker 51 to render the checking signal audible as a tone of characteristic pitch and thus provide a combination of periodic visual and audible signals within the locomotive for indicating proper operation of the equipment.

As has previously been described in connection with Figure 1, when the central station operator desires to transmit speech signals and depresses foot switch 32 the checking signals will cease for the duration of the speech transmission. Thus the checking signal will not interfere with the received speech transmissions. These speech transmissions will automatically be applied through the two-channel filter without appreciable attenuation to the loud speaker whenever they are transmitted from the control station.

The transmitter 52 when operated, ensures positive coordination between the control station operator and the locomotive engineer. Thus, the transmitter 52 permits the engineer of the locomotive to acknowledge the receipt of any specific instruction or to question any order and to ask for instructions whenever in doubt. The transmitter 52 also permits an engineer of one locomotive to communicate with an engineer of another radio-equipped locomotive in the same signalling zone.

The transmitter 52 is operable when the engineers transmitting switch 54 is actuated. Thus the actuation of switch 54 automatically energizes antenna transfer relay 55 to couple the antenna 5I to the output of the transmitter circuits 52.

In addition, the actuation of switch 54 will energize a power transfer relay 64 which operates in a manner similar to that of power transfer relay 33 which is disposed at the central control station.

Accordingly, when the transmitter switch 54 is actuated, the power transfer relay 64 disconnects the power source at the locomotive from the receiver and connects the transmitter to this source. Hence the locomotive engineer may, by speaking into microphone 65, call the operator of the central station at any time.

Ii, as previously mentioned, the locomotive engineer prefers to transmit a series of intermittent signals corresponding with a predetermined signalling code, he may by intermittently actuating the transmitting switch 54 key the transmitter to transmit a plurality of signals which will be made evident at the control station by the intermittent flashing of lamp 43. The power transfer relay serves in addition to transfer the energy from the receiver circuit to the transmitting circuit to energize a transmitting pilot lamp 66 to provide visual indication for the engineer that his transmitter is in operation.

This transmitter pilot light may also be disposed in the engineers field of vision. As shown in one modification, the transmitting pilot light 55 and the checking indicating light may be disposed upon the engineers microphone 85 which 10 in turn is always disposed in his field of vision as will be described in connection with Figure 12.

Thus, from the block-diagram representation of a control station and a coacting transmitting and receiving unit which may be disposed upon a movable vehicle it may be seen that two-Way voice communication may be established therebetween and that the operators of each station at all times have the additional protection afforded by the positive, selective action of visual indicators to show that the system is in proper working order.

To supplement the visual checking signal, the locomotive operator, as pointed out, also has an aural indication of reception of the checking signal. In the event of failure of any portion of the central station or mobile equipment, such failure will be visibly indicated at the central station and also on the locomotive through lack of visual or aural indication by the perodic checking signal.

Under these circumstances, the locomotive engineer and/or the control station operator will immediately investigate and will immediately cease all operations dependent upon the signalling system until the fault has been corrected.

An embodiment of the trafiic communication system schematically illustrated in Figures 1 and 2, particularly for adaptation to a classification yard or similar localized traffic area is more completely illustrated in Figures 3 through 12, and reference is now made thereto.

In Figure 3 there is shown a circuit diagram of one section of the control station schematically illustrated in Figure 1. The transmitter, as indicated, is energized from an alternating current supply impressed upon the terminals 1l. This alternating current is then rectified and applied to the transmitting circuits.

However, it is pointed out that any available power supply may be utilized and may be converted to the desired voltages in a manner which is well known in the art. The alternating current impressed upon terminals 1I is impressed upon a rectifier 12 through a power transformer 13, the high voltage secondary of which is joined to the anodes of the rectifier 12 in conventional manner.

A filament transformer 14 energizes the lament circuits of the various vacuum tubes and a pilot light 15 affords a visual indication of the application of this voltage.

Another secondary winding 16 is utilized to energize the heater of rectifier 12. The center tap thereof is the positive terminal of the direct current supply for the anodes of the transmitter. A filter 11 is employed to eliminate any ripple in the direct current supply. The alternating current impressed upon terminal 1l in addition serves to continuously drive a relatively small synchronous or other substantially constantspeed motor 8l which in turn drives a cam 82.

This cam, having a plurality of projections 83, operates to periodically close the switch 84 to permit the automatic keying of the transmitter as will be described in further detail. Essentially the transmitter comprises a radio frequency oscillator tube 85 having a tank circuit 81, the frequency of which is controlled by the crystal 86 in the grid circuit thereof.

The constant frequency output of the oscillator 85 is applied to the control grid of a power amplifier 92. The anode of this amplifier is energized from the high direct voltage source Uff.; l i

1 1 ll'n'ough a tank coil 93 and through a radio frcquency choke coil 94.

The output of the power amplifier is in turn coupled to thc antenna 23 through coupling condenser 05 and through antenna transfer relay 93. When the transmitter of Figure 3 is in the nor mal operating conditions as illustrated, the closure of switch 84 under the influence of cam 82 will, as illustrated, energize the coil 91 of the antenna transfer relay 06 to couple the antenna 23 to the output circuit of the amplifier 92, and so permit the radiation of the signal generated at the transmitter.

Energization of the relay coils is secured through a small rectifying unit |0| which is preferably of the dry-disc type energized through transformer |02 from the main alternating current supply.

As illustrated, an audio frequency control signal is impressed upon the input circuit ol the transmitter. This signal, which functions as the checking signal described in connection with Figures 1 and 2, is preferably of a relatively low frequency alternating current and is thus most conveniently obtained by utilizinga harmonic of the alternating current power supply.

Thus, as shown in Figure 3, thc audio frcquency control signal is obtained from the input to the lter 11. A tap on variable resistor |03 is coupled through condenser |04 and through the switch members of the input transfer relay 3| to the primary of the input transformer |05. The secondary of the transmitter input transformer |05 is coupled to the grid of a tube |06, the anodes of which are energized from the high voltage source through the primary of a coupling transformer |01.

The terminals of the secondary of transformer |01 are coupled to the grids of a push-pull modulator tube The anodes of the tube are joined to the terminals of the primary of a modulation transformer ||2, the center tap of which energized from the l'iigh voltage source.

In the modulating circuit, as indicated in Figure 3, the anode of the power amplifier 92 is coupled to the screen grid thereof through the tank coil 93 and the radio frequency choke 94. This parallel combination of screen grid and anode are then joined to the high voltage source through the secondary of transformer I2. Thus the signals impressed upon the input transformer |05 cause corresponding fluctuations in the plate and screen grid circuits of the power amplifier 92. The modulated carrier, as previously described` is coupled through condenser 95 to the antenna 23.

As hereinabove set forth, when relay 3| is in the normal position, the transmitter input amplier |06 is in a condition to be energized by the audio frequency energy tapped from power-supply resistor |03 and passed through condenser |04. and the switching members of transfer relay 3|. Thus, when power relay 33 is energized and power is applied to the transmitter, modulating signal energy is applied to the transmitter.

The audio frequency energy has a fundamental of twice the alternating' current input frequency and thus may be 0f the order of 120 cycles if av commercial power line is used for a power supply at the terminals 1|.

. When the various relays are in their normal position as illustrated in Figure 3, it may be seen that the switching members of power transfer relay 33 preclude the fiow of current in the primary of the plate transformer 13.

Accordingly, this precludes the energization of all the anode circuits of the transmitter since no voltage is impressed upon the anodes of the rectifier 12.

It is to be noted, however, that the transmitter is normally kept in a condition where immediate energization thereof may be effected. Thus the primary of the filament transformer 14 is continuously energized from the power impressed upon terminals 1|. The plate transformer 13 is dependent upon the position of the switching members of the power transfer' relay 33 for energization.

During the rotation of motor 8l, the cam projection 83 will close switch 84 and as may been seen from the circuit diagram, will thereby energize the coil of power transfer relay 33 from the voltage provided by the small full wave rectifier |0|, provided, of course, that the coil of lockout relay 42 remains deenergized and the switch contacts thereof remain in the position illus trated in Figure 3.

Energization of power transfer relay 33 will cause the switching members 33 to move downward as viewed in Figure 3 and accordingly will energize the primary 13 of the plate transformer. This will simultaneously cause the application of a high direct-current potential to the anode of the various vacuum tube circuits illustrated and supply the low frequency signal to the primary of input transformer |05.

The coil 91 of the antenna transfer relay 24 is in parallel with the operating coil of power transfer relay 33 and consequently when the switch 84 is closed by the cam 82, the antenna transfer relay will operate to cause thc arm 24 to move downwardly as viewed in Figure 3 and connect the antenna. 23 to the tank coil 93 through coupling condenser 95.

Therefore, the carrier modulated by a constantamplitude audio frequency control signal is radiated into space when switch 84 is closed. Since the filaments of the various electron tubes are normally heated in this power transfer system, the transmitter will operate instantaneously upon the closure of switch 84.

Continued rotation of the cam will open the contacts of switch 84 and deenergizc thc relays 33 and 24 which will then resume their normal positions indicated in Figure 3 and the transmission of a wave will cease. Since, as previously described, the motor 8| operates at a substantially constant speed, the closure of switch contacts 84 will be periodic and thus a periodic signal comprising a radio frequency carrier modulated by an audio frequency signal will automatically be transmitted.

The rate at which these periodic signals are transmitted is dependent upon the particular applical-ion. As mentioned in connection with the block diagrams of the cent1-a1 station and the mobile station, Figures 1 and 2 respectively. the periodic impulses of the type just described arc utilized as a checking' signal in order that the operators may have positive indication that the system is in proper working order.

Since, however, it is desirable in this novel system to permit the operator of the mobile station to call and speak to the control station, these pulses are of relatively short duration and may normally be transmitted at regular intervals of, for example, the order of five seconds apart.

Since the operation of the power transfer relay 33 is periodic in accordance with the operation it-arti:

of switch contacts 84, the application of power to the transmitting circuits periodically occurs for a relatively short time. Therefore, since the modulated carrier of the transmitter is only generated for relatively short intervals, considerable economies are effected and the consumption of electrical energy is greatly decreased.

As hereinabove described, the monitor pilot light 35 shown in Figures 1 and 3 provides a visual indication of the fact that a modulated carrier is being generated. Energy for the operation of the relay controlling the pilot light 35 is derived from inductive coupling with the tank circuit of the transmitter. As illustrated in Figure 3, a coil |2| is inductively coupled with the tank coil 93.

The coil |2| is tuned to the carrier frequency by the variable condenser |22 and the potential appearing across this tuned circuit is impressed through the parallel combination of grid leak |23 and condenser |24 upon the control grid of an electron tube |25 which functions in this instance as a grid-leak detector. The anode circuit of the tube |25 is joined to the source of high potential through load resistor |26 and the output of this tube is coupled through condenser |21 to the anodes of a signal rectifier |3|.

The rectified modulating signal energy then flows through the coil of the monitor relay 3l to cause the operation of contacts 3l thereof. The contacts 31' are joined in series with the monitor light 35 and this series circuit is` connected t0 a power source suitable for energizing the monitor light 35.

In the embodiment illustrated in Figure 3, the monitor light is of a relatively low voltage type and is energized from the filament supply obtained from transformer secondary 14. A condenser |32 is connected across the monitor light in order to prevent radio frequency energy, which may be present in the relay leads due to stray coupling, from being fed back into the input circuit by interconnecting cables.

Since the coil of relay 3l is energized by the rectified demodulated energy coupled from the tank circuitY the monitor pilot light will ash, whenever a modualted carrier is generated and a signal transmitted. The relay 31 will normally tend to follow the variations of the modulations which may, if desired, be smoothed as desired by a filter circuit to preclude chattering thereof. A condenser, |33, is placed across the winding of relay 3l to by-pass the alternating current component of the rectified audio frequency signal.

The transmitter pilot light 4| is energized through the switching members of the power transfer relay 33 from the filament supply of the transmitter. This light will therefore operate whenever plate power is applied to the transmitter circuits and thus during the normal operation of the central station will ash periodically in accordance with the closing of switch 84.

If the central station operator desires to transmit a message to the operator of a locomotive in the classification yard. the switch 32 is closed. This switch may be any conveniently disposed normally open switch and in the modification illustrated, it is a foot switch adjacent the transmitter.

Closure of this switch will apply energy from rectifier |0| to the coil of input transfer relay 3| and accordingly cause the switching members 3| thereof to move downwardly and, as indicated, to interrupt the control signal circuit from the tap on power-supply resistor |03 to the input transformer |85, and to complete the circuit from a microphone 26 to this input circuit.

In addition, the switching members of this relay complete a circuit from the high voltage point of rectifier |8| to the parallel coils of relays 33 and 91, provided relay 42 is not energized. These relay coils, when energized as previously described, will apply a high potential to the plate circuits of the various vacuum tubes at the transmitter and will connect the antenna 23 to the tank circuit of the transmitter. Thus, the transmitter is in a condition whereby speech energy impressed upon microphone 26 is amplified and caused to modulate the radio frequency carrier in power amplifier 92, the energy from which is then radiated into space through antenna 23.

Furthermore, the operation of relay 3| in disconnecting the source of constant amplitude audio frequency checking signal from the input circuit of the transmitter precludes interference between speech transmission and the checking impulses despite the continued operation of motor 8| and the continued closure of switch 84.

Therefore, the operator of the central control station may transmit a message by operating the switch 32 and speaking into microphone 26. Since the receiver at the mobile unit is normally in a position for the reception of energy` the operator of the central station may immediately establish communications with the operator of a mobile unit within the same signaling zone.

The receiver of the central station permits the reception of signals from the classification yard locomotive whenever the engineer thereof desires to call in, check instructions, or acknowledge an instruction. This receiver is normally in a position whereby energy transmitted from the locomotive station may be received.

The central station receiver, illustrated in Figure 4, and in the block diagram, Figure 1, is related to the central station transmitter illustrated in Figure 3 in that a common antenna may be employed in both circuits and that power for the operation thereof is sequentially applied in a predetermined periodic signalling cycle as determined by the operation of synchronous motor 8| and associated cam 82.

The power transfer relay 33 illustrated in Figure 3 is common to the receiver and to the transmitter and these are interconnected between the terminals |4|. Furthermore, the common antenna 23 illustrated in Figure 3 is connected to the receiver through antenna transfer relay 24 and through a connection joined to terminals |42|42 at the receiver and transmitter.

When the power transfer relay 33 and the antenna transfer relay 24 are in the position indicated in Figure 3, the receiving circuits are energized and the antenna 23 is joined to the input circuits and thus places the receiver in a condition for the reception of signals intercepted by the antenna. The receiver may be energized from an individual rectifying circuit energized from the same source of alternaitng current and impressed upon the receiver terminals |43.

The plate transformer |44 and the filament transformer |41 are continuously energized from the terminating current source |43. Conventional filter section |46 is joined to the filament of the rectifier |45 for eliminating the ripple of the rectified potential. A bleeder resister |48 is shunted across the output of the filter section |46. The high potential lead for energizing the plate circuits of the various electron tubes is broken at |4| by means of normally closed contacts 33" on the power transfer relay 33 as indicated in Figure 3. The interconnection of Figures 3 and 4 is shown by the corresponding terminals |4| on both signals.

The filaments (not shown) tubes indicated in Figure 4 are all continuously energized from the power transformer secondary |41 and thus, as shown, in Figure 4, power is applied to both anode and heater circuits of the receiver.

Incoming signals intercepted by the antenna 23 are impressed upon a radio frequency transformer |5| the secondary of which is tuned by a variable condenser |52. A radio frequency amplifier |53 of conventional form is utilized to raise the level of incoming signals and the output thereof is coupled through condenser |54 to a grid of converter tube |55.

A beat frequency oscillator tube |56 utilizing a crystal |51 for frequency control generates a continuous oscillation which is coupled from coil |6| to another grid of the converter tube |55. This radio receiving circuit may comprise the conventional superheterodyne circuit for receiving and demodulating incoming signals. Thus, the output of the converter tube is coupled through an intermediate frequency transformer |62 to the control grid of an amplifier |63.

The output of this last mentioned amplifier |63 is then coupled through the intermediate frequency transformer |64 to a second amplifier tube |85. This tube has a diode section energied through condenser |61 and having a load resister |68 which furnishes a negative biased voltage for automatic volume control as is well known in the art. The output of the amplifier tube is also coupled to intermediate frequency transformer |61 to one anode |10 of the double diode rectifier tube |68. The variable potentiometer |1| acts as a diode load and is coupled through condenser |12 to the grid |13 of the dual triode |8|.

The diode load |1| is bypassed by condenser |14 which acts as a radio frequency filter. This diode load |1| is also shunted by the other diode section of the tube |66, and condenser |15. This acts as a noise discriminating and limiting circuit. 'Ihe arm of the potentiometer |1| is connected to grid |16 of the dual triode tube |8| through the filter resistor |11. When no carrier is present the grid |16 is at zero potential with respect to its associated cathode and therefore the effective plate resistance is very low. By means of the voltage dividing network comprising resistors and |93 the grid |13 through its gridleak |19 is maintained at a high negative voltage with respect to its associated cathode. This high negative bias effectively reduces the amplification of the tube to a minute value and causes a cessation in the flow of plate current. When a carrier is present and amplified by the respective radio frequency and intermediate radio frequency amplifiers and rectified by means of the diode |66 a negative voltage appears across potentiometer |1|. This voltage when applied from the adjustable arm of the aforementioned poteniometcr to the filter resistor |11 through the grid |16 of the dual triode I8| causes the plate resistance thereof to increase considerably in value. This by means of the aforementioned voltage dividing network causes the grid |13 to assume its normal operating bias with respect to its associated cathode. Thus, audio-frequency noise suppression is effected, under control of an incoming radio frequency carrier.

of the electron` Therefore, plate current will flow through |82 and through the relay 42 causing the switching members to operate. Since the winding of the relay 42 has a high impedance to audio-frequencies, this winding together with the compensating resistor |92` acts as the plate load for |82 and thus the audio-frequency signals are coupled by means of condenser |83 and volume control |84 to the input grid of the power amplifier tube |85.

The output of amplifier |85 is coupled through transformer |81 in the anode circuit thereof to the loud speaker 25 and to a jack |9| to which earphones may be connected if desired.

The anode |82 is energied from the high positive potential through a parallel combination of the load resistor |92 and the coil of suppressor relay 42. An incoming carrier intercepted by the antenna 23 and amplified and demodulated in the various receiver circuits illustrated in Figure 4 will thus cause the cnergization of the coil of relay 42 to cause the movement of switch members 42.

This novel manner of actuating a lock-out relay 42 inserted in an audio-frequency noise suppression circuit in accordance with an incoming radio frequency carrier is illustrated in both Figures 3l and 4 and the various connections of the switching members are best illustrated in Figure 3. Thus it may be seen that the energization of the coil of relay 42 due to a received signal will cause the movement of the switch members to open the series circuit of switch 84 and contacts 8| between the coils of relays 33 and 24.

Accordingly, the continued operation of the switch 84 under the influence of the cam 82 will have no effect upon these circuits. The operation of the switch members of suppressor-actuated relay 42 also completes a circuit from the filament winding 14 of the power transformer to the call light 43 and thus when a signal is received, the calling light will flash. An incoming signal will operate lock-out relay 42 as previously described to preclude the operation of power transfer relay 33 and antenna transfer relay 24 from the positions indicated in Figure 3.

Therefore, the reception of a signal will preclude the transmission from the central station of the checking impulse or speech transmission which would normally tend to interfere with the signal received. As the antenna 23 is alternately switched from the receiver circuit to the transmitter circuit, reception will only take place when in the position shown in Figure 3. This permits the operator of a classification yard locomotive. by the mere transmission of his carrier wave to maintain the central station in condition for receiving signals.

The engineer may transmit speech signals from his vehicle transmitter which will be made audible through the agency of the central station loud speaker 25. Or he may be merely keying his carrier in accordance with a predetermined code, cause the calling light 43 to ash correspondingly.

When the opera-tor of the mobile unit deenergizes his transmitter, the lock-out relay 42 automatically is deenergzed and permits the switching member 42 to assume the position indicated in Figure 3, which thus permits keying of the central station carrier wave in accordance with et.; ci; ferilli audios 17 described in connection with Figures 3 and 4 utilizes a single antenna for the transmission and reception of signals.

It is pointed out that various known forms of transmission systems may be utilized in connection with a classification yard traffic coordination system of the nature being described. Thus the receiver and transmitter units at both the central station and'the mobile station within a locomotive may be of the ultra high frequency type employing directional radiations or nondirectional radiations.

This of course constitutes no limitations whatsoever since the various longer wave transmission systems may be utilized, if convenient. This will merely necessitate a modification of the modulators and amplifiers. Furthermore, the common antenna illustrated may be dispensed with and an individual antenna employed for the receiver circuit and the transmitter circuit.

If a separate antenna is employed it will eliminate the need for antenna transfer relay 24 and the circuit connections which are necessary to cause the proper energization thereof as described.

However, with an ultra-high frequency system of the illustrative type described herein, a single communications channel may be employed for both transmitter and receiver. This is preferable in the illustrative case, since it permits the employment of a single tuned antenna circuit of high efficiency for both units.

On the other hand, a distinct carrier frequency may be utilized for each station and the circuits necessary for demodulation and transmission may be varied accordingly as is well known in the art. It is also possible with the general system disclosed in connection with the central station unit illustrated in Figures 3 and 4 to utilize the technique of localized traffic lane signalling within a restricted locality disclosed in copending application Serial No. 260,644, filed March 8, 1939, Patent No. 2,255,055 granted September 9, 1941.

As disclosed in copending application Serial No. 260,644, now Patent No. 2,255,055, electric wave signalling may be effected in a localized area along a traffic lane by means of a transmission cable disposed within the area for the extent of a signalling zone.

The mobile unit to be described in connection with block diagram Figure 2 and subsequently to be described in connection With Figures '7 and 8, may of course utilize any of the aforementioned signalling channels. The receiving circuit illustrated in Figures 'l and 8 corresponds with the diagrammatically illustrated mobile receiver of Figure 2 and similar reference numerals will be carried over to designate similar elements.

This mobile station may, if used upon the classification yard locomotive, be most conveniently disposed upon the tender with connections to a microphone and a loud speaker and necessary switching equipment within the locomotive cab. The station comprises essentially a transmitter and a receiver cooperating with antenna 5| which may be of a coaxial type. During normal operating conditions the receiver is continually energized and the antenna is joined thereto in order that any signal transmitted from the central station be immediately apparent within the locomotive cab.

Thus, as shown, through antenna transfer relay 55, the antenna 5| is coupled to the input radio frequency transformer of the receiving circuit. The receiver is substantially similar to lil 18 that utilized at the central station and illustrated in Figure 4.

The power required for driving the various transmitting and receiving circuits illustrated in Figures 'l and 8 is obtained from a locomotive electrical power supply which is a conventional 32 volt direct current supply. This supply is utilized to continuously energize all of the filaments of the combined circuit in accordance with circuit 202.

The variable resistor 203 is inserted in series with the filament circuit 202 and the direct current impressed upon terminals 204. To obtain the required voltage for driving the plate circuits of the various tubes, a small motor generator, employing a motor unit 205 is utilized to drive a directly-coupled generator 206 to generate the required voltage.

This voltage is filtered by the circuit of chokes and condensers 201 to remove any commutator ripple or the like. The output high direct-current potential is then selectively impressed upon the plate circuits of the receiver or the plate circuits of the transmitter as determined by the position of power transfer relay 64 which operates simultaneously with the antenna transfer relay 55. As shown, the high direct-current potential is coupled to the anode circuits of the receiver electron tubes and the antenna 5| is coupled to the input transformer 20|.

The receiver comprises essentially a radio frequency amplifier 2|| energized by the potential developed within the tuned radio frequency input circuit 20|. The anode of this radio frequency amplifier is energized from the high potential generated by the motor generator 205, 206 and the output thereof is coupled through circuit 2|2 to one grid of a converter tube 2|3.

A heterodyne oscillator 2|4 utilizes a tuned circuit 2|5 and a crystal 2I6 for determining the frequency thereof and the continuous frequency output thereof is impressed through coupling condenser 2|`| upon another grid of the converter 2 I 3.

The beat frequency component of the output of converter 2|3 is selected and coupled to the intermediate frequency amplifier 22| by an intermediate frequency transformer 222. This amplifier operates in conventional manner and the output thereof is coupled through intermediate frequency transformer 223 to the input of the diode-pentode tube 224 which in turn is coupled to the automatic volume control circuit and a demodulator and noise limiter as hereinabove described in connection with the central station receiver illustrated in Figure 4.

The demodulated output of this receiving circuit is then coupled to a double triode electron tube 22B one section of which functions to amplify the audio-signal. The other section of tube 226 acts as a suppressor circuit as described in connection with the similar circuit of Figure 4. The signal is then coupled through condenser 231 to a power amplifier 24| the output of which is coupled through transformer 242 to an earphone connection 243 and a parallel two-channel filter f illustrated in Figure 8) through the terminals 3 and 4 of the connector 244 illustrated in both Figures 7 and 8.

Referring now to Figure 8, the filter section comprises essentially a parallel arrangement of high pass and low pass filter sections joined to the terminals 3 and 4 of the connector 244. Thus a low pass filter which may in one form comprise series chokes 245 and shunt condenser 246 will effectively block the passage of high frequency signals while permitting the unimpeded passage of low frequency signals therethrough.

The high pass filter in parallel with the low pass filter section joined to terminals 3 and 4 of connector 344 comprises essentially a plurality of series condensers 241 and shunt inductance 25|. This filter section then will preclude the passage of relative low frequencies while permitting the unimpeded passage of the higher frequency signals. The design of the filter will determine the extent to which attenuation of signals of various frequencies may be effected. Hence the high pass filter section may be designed to pass a relatively small amount of low frequency energy to permit limited aural reception of the checking signal, if desired.

Accordingly, demodulated energy applied to the terminals 3 and 4 from the output of the power amplifier 24| will selectively pass through filter circuits depending upon the nature of the signal. If the received signal comprises the low frequency checking impulses periodically transmitted from the central station in the manner described in connection with Figures l, 3 and 4, then the 10W pass filter section will permit the passage of the demodulated currents which will then be impressed upon full Wave rectifying unit 252.

This rectier may comprise a small dry-disc bridge as indicated, and the low frequency checking signal will be rectified therein and as illustrated, the output thereof is impressed upon the coil 253 of the checking signal relay 62 illustrated also in Figure 2.

Since the current is of a fluctuating nature,

mitted from the central station periodically due to the operation of synchronous motor 8|' and correspondingly switch 84 will be received at the locomotive in the classification yard and will be demodulated and amplified and impressed upon a relay 62.

The switching member 62 of this relay will therefore operate in a manner which corresponds with the operation of switch 84 during normal operation of the two-way signalling system. The closure of relay 62 as indicated in Figure 8 will short-circuit a section of a variable resistor 26|. This resistor 26| is joined in series through terminals and 2 of connector 244 indicated in Figures 'l and 8, with a checking pilot light 63 and the entire series circuit is connected between the direct current supply of the locomotive and ground.

Therefore, the checking pilot light 63 is continuously energized by the passage of current therethrough, this current being determined by the magnitude of resistor 26|.

Upon the receipt of a checking signal, the contacts of checking relay 62 are closed and a section of the resistor 26| is short-circuited as determined by the position of the variable tap 263. Therefore, the checking light will iiash to full brightness upon thereceipt of a checking impulse and indicate in the manner described, the proper operation of the transmitting and receiving circuits. The output of the high pass filter comprising the condensers 241 and the choke 25| is coupled through transformer 264 to the loud speaker 51.

A received speech transmission will pass through the high pass filter section and energize the loud speaker and so permit the central station operator to instruct the operator of the classification engine. The speech transmission will not effectively flow through the low pass filter and thus will not energize the checking lamp.

The checking signals may, as described above, be permitted to energize the loud speaker 51 to provide an audible check on the operation of the trafc communication system. Thus the checking signals will periodically cause the flashing of the lamp and simultaneously cause a distinctive checking or proceed tone to be heard from the loud speaker.

Since the checking signals are automatically cut out at the central station, as described, when speech is being transmitted, the checking signals will not interfere audibly with this speech. The locomotive engineer is provided, by the apparatus illustrated in Figures '1 and 8, with a transmitter for calling and speaking to the central station operator. The filaments of this transmitter are normally energized from the locomotive 32 volt supply. The plate circuits thereof are normally deenergized and the antenna 5| is normally uncoupled therefrom.

When the engineer desires to call the central station, he may depress his transmitter switch 54 which, as illustrated in Figure 7, joins coil 21| of relay 212 between the direct current source available and ground. A resistor 213 reduces the flow of current in the relay Winding to prevent damage to the relay coil 21|.

In addition, the operation of switch 54 energizes the coil 214 of the antenna transfer and power transfer relays 55 and 64 respectively, and thus causes the consequent movement of the switch arms which in turn connects the antenna 5| to the output of the transmitting circuits and applies the high potential available from the generator 206 to the transmitting anode circuits and disconnects this potential from the receiver circuits.

The energization of relay coil 21| causes the movement of the switching members 212' downf wardly as viewed in Figure '1 to close their respective circuits and as indicated, complete one circuit from the positive terminal of the direct current available at the terminals 204 through the switching member and through a variable resistor 216 to ground.

The variable tap of the resistor 216 then is joined in circuit through the primary of the transmitter input transformer 215, through the microphone to ground. Thus an energizing potential is impressed upon the microphone 65 which is preferably of the carbon type since relatively high gain is obtained immediately at the microphone.

The other switching member of the relay 212 short circuits a section of a variable resistor 28|. This resistor is in series with a transmitting pilot light 66 and the series combination is joined to the terminals 264. The resistance in the transmitting pilot light circuit presented by resistor 28| is normally sufficiently great to preclude the illumination of transmitting pilot bulb 56.

However, upon the operation of relay 212 and the short circuiting of a section of the resistor 28 I, the lamp 66 glows to indicate that the transmitter is being energized. The transmitter may be of any conventional form and, as illustrated, essentially comprises an oscillator 282 having a tuned circuit 283 and a crystal 284 for determining the frequency thereof.

The output of the oscillator is coupled to the control grid of a power amplifier 205, the plate circuit of which is energized from the high potential source through inductance 286 and through radio frequency choke 201 and tank inductance 29|. The screen grid of the power amplifier 285 is also energized from the high potential source through inductance 286 and through resistor 292.

Sound waves, when impressed upon the carbon microphone 35 establish corresponding electrical fluctuations which are impressed upon the primary of transformer 215 and cause corresponding electrical variations in the secondary thereof which is joined to the control grid of modulator tube 295.

The screen grid of thc modulator 295 is joined to the high potential source and the plate circuit thereof is joined thereto through the inductance 286. The amplified signals which appear in the output circuit of the modulator 295 modulate the radio frequency carrier generated by the oscillator 282 and its associated crystal 2-84.

Thus when speech is impressed upon the microphone 65 and the switch 54 is closed, the antenna 5| will radiate a carrier modulated in accordance with the speech. If no speech is impressed upon the microphone the carrier only will be radiated. The radiated signals will be received at the receiver illustrated in Figure 4 at the central station and in the time intervening between two successive checking impulses, the radiated carrier or modulated carrier will cause the suppressor relay 48 of the central station to operate to preclude the further transmission of checking signals.

This traiiic communication system may be employed Wherever mobile units are operated in a localized signalling area. Where applied to railroad work and more specically to classification yards at freight stations, the elements of the apparatus may preferably be arranged as illustrated in Figures 5, 6, 9, 10, 11 and 12.

Thus at the central control station, we may incorporate the loud speaker, microphone and indicating lights into a single compact unit as illustrated in Figures 5 and 6. The loud speaker 25 is mounted within a housing 30| in a position slightly above ear-level where sounds may most easily be detected. A exible or non-exible arm 302 supports the microphone 26 within a housing 303 attached to the arm at 304.

In addition, the housing also provides supporting means for the three indicating lights at the central station schematically illustrated in Figure 1 and in the circuit diagrams of Figure 3. These lights may be of a distinctive color and are energized through the necessary wiring indicated in Figure 3, this wiring being carried through the flexible -arm 302.

The entire assembly of microphone, loud speaker and checking lights may be disposed at a central control point within the station which, in turn, may be located adjacent the hump of the classification yard.

If the operator is in an elevated position, with respect to the hump, in a control tower, then the microphone and loud speaker assembly indicated in Figures 5 and 6 may be disposed adjacent a window overlooking the yard. The foot switch 32 which, when depressed, permits the transmission of speech from the central station, may be disposed directly beneath the combined microphone and loud speaker assembly.

The central station operator will always have the microphone available for speech transmission and, by merely depressing the foot switch. may call a locomotive within the classication yard and relay the required instructions. Furthermore, at all times the three indicating lights, 4|, 43 and 35 will be in his lield of vision in order that he may ascertain the correct operation of the system.

Since the operator will always be near the microphone and loud speaker assembly, the calling of a locomotive engineer will immediately be apparent to the central station operator who will then acknowledge this call and confer with the locomotive engineer.

As indicated in Figures i9, 10 and 1l, the microphone of the mobile unit may be of similar construction. Thus the microphone 65 is supported upon a flexible arm 3|| which in turn is carried upon a support 3|2 which may be secured to the roof of the locomotive, or other vehicles, by a plurality of screws 3|3.

The microphone in this embodiment is mounted within a shock-resistant housing in order that the vibration and the like experienced by the locomotive will not injure the sensitive microphone nor cause undue transmission of noise.

Thus, as indicated in Figur-e 10, the microphone 65 is supported substantially centrally within a housing 3|4 which is joined to the flexible arm 3| at 3|2.

The exible arm carries the necessary microphone wires 3|5 therethrough to permit the energization thereof and the transmission of speech currents. The relatively large space between the microphone and the outer wall of the supporting housing 3|4 is packed with a highly-resilient material 3|6 or the like in order that the jarring of the housing will be effectively damped and not transmitted to the microphone itself.

The indicating lights 63 and B6 at the transmitter, which visually indicate the checking signal and show that the locomotive transmitter is in operation, may be mounted upon the microphone in order that the engineer when speaking, may have a visual indication of the condition of the various system elements. The mounting of the microphone is most clearly illustrated in Figure 12, which is a pictorial illustration of the interior of a locomotive cab.

The engineer, as is well known, normally must observe the roadway in performing the various operations and cannot conveniently employ his hands to hold a microphone. Thus, we prefer to suspend the microphone directly within the engineers eld of vision by means of the exible arm 3| by securing the support 3|2 to the roof of the cab, and extending the flexible connector so that it projects inward with respect to the window 32| of the locomotive.

The directional loud speaker 51 employed within the locomotive cab may be disposed behind the engineers seat 322 and directed towards him so that the speech signals will readily be audible. Accordingly, the engineer will receive transmitted speech signals by loud speaker 51 and will at all times have the checking signal in his eld of vision to ascertain the proper working order of the complete communication system.

The transmitting switch 54 may be disposed adjacent the sash of the window 32| in order that the engineer may conveniently operate this switch without moving from his normal position. Since the microphone, as was previously mentioned, is directly within his eld of vision, he will at all times be able to observe operation of the checking or proceed signal and transmitting pilot light indicators.

It will now be obvious that various modifications of this specific disclosure will be evident to those skilled in the art. Accordingly I prefer not to be bound by the specific disclosure above but by the appended claims.

I claim:

1. In a traffic signaling system for effecting automatic supervisory signalling between a station and a remote mobile unit, a carrier wave transmitter for said station, a second carrier wave transmitter for said remote mobile unit, carrier wave receiving means individual to said station and responsive to carrier wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and responsive to carrier wave energy from said station, a source of control signal energy, means for intermittently effecting emission of a control signal modulated carrier wave by said station transmitter, a trans fer means for said mobile unit adapted to render effective either the carrier wave transmitter or the carrier wave receiving means of said mobile unit and switching means coupled to said transfer means and operable for actuating said transfer means to initiate operation of the carrier wave transmitter of said remote mobile unit during' a period between intermittent transmission of carrier wave energy by said station.

2. In a traffic signaling system for effecting automatic supervisory signaling between a traffic control station and a remote mobile unit, a carrier wave transmitter for said traffic control station, a second carrier wave transmitter for said remote mobile unit, carrier wave receiving means individual to said traffic control station and responsive to carrier wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and responsive to carrier wave energy from said traic control station, a source of control signal energy, means for intermittently effecting emission of a control signal modulated carrier wave by said traflic control station transmitter, a transfer means for said mobile unit adapted to render effective either the carrier wave transmitter or the carrier wave receiving means of said mobile unit and switching means coupled to said transfer means and operable for actuating said transfer means to initiate operation of the remote mobile unitl carrier wave receiving means individual to said traffic control station and responsive .to carrier wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and responsive to carrier wave energy from said traffic control station, a source of control signal energy, switching means for periodically effecting emission of a carrier wave by said traffic control station transmitter and simultaneously impressing said control signal energy on said carrier wave, a transfer switch for said mobile unit adapted to render effective either the carrier wave transmitter or the carrier wave receiving means of said mobile unit and switching means coupled to said transfer switch and operable for actuating said transfer switch to render effective the carrier wave transmitter of said remote mobile unit during periods between periodic transmission of carrier wave energy by "i, said traffic control station.

4. In a traflc signaling system for effecting automatic supervisory signaling lbetween a traffic control station and a remote mobile unit, a carrier wave transmitter for said traffic control station, a second carrier wave transmitter for said remote mobile unit, carrier wave receiving means individual to said trafila control station and responsive to carrier wave energy from said mobile unit, carrier wave receiving means individual to said mobile unit and responsive to carrier wave energy from said traffic control station, a source of audio frequency control signal energy, automatic switching means for periodically effecting emission of a carrier wave by said traffic control station transmitter and simultaneously impressing said control signal energy on said carrier wave, a transfer relay for said mobile unit adapted to render effective either the carrier wave transmitter or the carrier wave receiving means of said mobile unit and switching means coupled to said relay and operable for actuating said relay to render effective the carrier wave transmitter of' said remote mobile unit during periods between periodic transmission of carrier wave energy by said traffic control station.

WILLIAM S. HALSTEAD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,587,121 Harlow June 1, 1926 1,891,299 Anderson et al Dec. 20, 1932 2,028,497 Clausing et al Jan. 21, 1936 2,131,042 Halstead Sept. 27, 1938 2,189,549 Hershberger Feb. 6 1940 2,206,231 McKay July 2, 1940 2,214,101 Cumming Sept. 10, 1940 FOREIGN PATENTS Number Country Date Great Britain Nov. 23, 1933` 

